Introduction

Herbal medicines are the promising choice of modern day drug discovery experiments. It gives detailed information on how to treat ailments with herbals and exemplifies new platform for drug discovery. The sacred Vedas dating back between 3500 B. C and 800 B. C give many references of the utilization of the medicinal plants. It has been mentioned in Rig Veda', about the use of Cinnamon (Cinnamom umverum), Ginger (Zingiber officinale) and Sandalwood (Santalum album) in the religious ceremonies and in the medical preparations (Parekh & Chanda, 2007). For the past few years, extensive research activities are focusing on identifying functional foods that can aid to manage the oxidative stress in the cell. Functional foods are the potential warrior against long term illness and additionally helps to meet the nutritional balance (Medoua, 2009). Traditionally, Glycyrrhiza glabra (Figure 1) is included in various medical preparations as an expectorant, sweetener, demulcent and laxative. Indian, Chinese, Egyptian, Greek and Roman civilization have been using dried rhizome and root of Glycyrrhiza glabra as medicinally important constituents.

Ginger is scientifically known as Zingiber officinale (Figure 2) belongs to the family, Zingiberaceae which has identified to contain 85 species of medicinal plants from East Asia and tropical Australia (Amiril, 2006). The root or rhizome that is used for cooking and therapeutic commitments.

Glycyrrhizin, the compound present in Glycyrrhiza glabra is in commercial use as a flavoring agent and sweetener (Wang, 2000) . For many years, Glycyrrhiza glabra has been used to treat ulcers, dyspepsia and allergenic reactions (Ammosov & Litvinenko, 2003). Ginger has been proven for its triggering roles in immune response (Harikrishnan, 2011). Ginger contains natural organic materials that facilitate growth, anti-stress, environmentally friendly and antimicrobial properties (Maqsood, 2011). The gingerol present in Ginger has been characterized well for its antimicrobial, anti-sedative and antipyretic roles.

Phenolic compounds are secondary metabolites found in plants. Phenolic acids are always found in association with other metabolites in plants. Phenolic acid increases bile secretion, reduces blood cholesterol and lipid levels and antimicrobial activity against some bacteria (Gryglewski, 1987). The flavonoids exhibit a wide range of biological effects including antibacterial, anti-inflammatory, anti-allergic and anti-thrombotic actions. The epidemiological studies point out their possible role in preventing cardiovascular diseases and cancer. Flavonoids play a crucial role in the management of oxidative stress management on macromolecules such as carbohydrates, proteins, lipids and DNA (Atmani, 2009).

The major active components of Zingiber officinale (Figure 3) include 6-gingerol, 6-shogaol, and 6-paradol. Oleoresin comprising of non-volatile pungent principles gingerols (mainly [6]-gingerol). Volatile oil containing sesquiterpene hydrocarbon viz zingiberene, sesquiphellandrene and curcumene as major constituents. The pungency of Ginger is due to an alcoholic group of the oleoresin gingerol and zingerone (5 to 8%). Bisabolene, zingiberene and zingiberol are the major volatile compounds responsible for the aroma.

Glabridin, found in Glycyrrhiza glabra, is an isoflavane, a type of isoflavonoid. Glabridin is a yellowish-brown powder, insoluble in water, but soluble in organic solvents such as propylene glycol. The main objective of this study was to evaluate the phenolic compounds present in both Zingiber officinale and Glycyrrhiza glabra. The antioxidant potential of both plants was also studied by in vitro assays.

Materials and Methods

Plant source

The roots of Glycyrrhiza glabra and Z ingiber officinale were collected from the in and around villages of Kanchipuram, Tamil Nadu, India. The roots were dried for 10-12 days in the shadow, ground into a fine powder and stored. Using 5gm of powder, ethanolic and chloroform extracts were prepared.

Test for Phytochemicals

The major secondary metabolites available in the plant extracts are identified by standard methods (Doss, 2016; Harborne, 1973).

Quantitative Analysis

100 mg of the plant sample was homogenized with 1.0 ml of 0.5 M phosphate buffer (pH 6.9). The level of ascorbic acid (Omaye, 1979), Tocopherol (Baker, 1988), Flavonoids (Lin & Tang, 2007), Total Phenol Compounds (Lin et al., 2007), Catalase (Beers & Sizer, 1952), Superoxide Dismutase (Beauchamp & Fridovich, 1971) and DPPH assay (17) (Mohanasundaram et al., 2019) were performed as per the standard proven methods.

UV Spectrophotometry Analysis

The Glycyrrhiza glabra and Zingiber officinale fresh roots were extracted and analysed by UV spectrophotometer at the wavelength range between 200 and 500nm and the spectra obtained were analysed by comparing with the UV spectra of standard phenolic compounds and flavonoids.

FT-IR Analysis

The Glycyrrhiza glabra and Zingiber officinale roots were dried at 60ºC and made into powder. 2mg of the sample was added with 100mg of KBr and pressed into a disc of 3mm thickness. The disc was observed in the wavelength range between 500 and 3500cm^-1.

Results and Discussion

The ethanol and chloroform extracts of Glycyrrhiza glabra and Zingiber officinale roots shows (Table 1) the presence of important metabolites as phytochemicals constituents. Glycyrrhiza glabra is an important ingredient of herbal formulation used for the treatment of many diseases like rheumatism, hemorrhagic diseases, etc. (Kaur, 2013). Because of the presence of notable secondary metabolites, the extract shows antimicrobial activity (Sugumar, 2019). Phenolic compounds have crucial roles in the antioxidant and antimicrobial properties and hence the plant was identified with antimicrobial activity (Matasyoh, 2007).

Table 2 shows the levels of flavonoids and phenolic compounds in Glycyrrhiza glabra and Zingiber officinale roots. The results show significant levels of flavonoids and phenolic compounds in Glycyrrhiza glabra and Zingiber officinale roots. The more important compounds of Glycyrrhiza glabra are glycyrrhizin and glycyrrhizic acid, which are believed to be responsible for anti-ulcer, anti-inflammatory, anti-diuretic, antiepileptic, anti-hepatotoxic, anti-viral, antiallergic and antioxidant properties of the plant (Al-Qarawi, 2001; Arystanova, 2001).

Table 4; Table 3 show the levels and activities of antioxidants in Glycyrrhiza glabra and Zingiber officinale roots. The results show significant levels and activities of antioxidants in Glycyrrhiza glabra and Zingiber officinale root tissues. Glycyrrhiza glabra L is identified with huge antioxidant activity (Visavadiya, 2009). The flavonoids and phenolic compounds present in Ginger are strong anti-oxidant substances and considered a safe herbal medicine (Rehman, 2011). This antioxidant potential was further confirmed by the DPPH assay of both plant extracts.

Figure 5; Figure 4 show the results of standard ascorbic acid, Glycyrrhiza glabra and Zingiber officinale used in DPPH assay. Our results show a significant DPPH scavenging activity of Glycyrrhiza glabra and Zingiber officinale roots tissue.

The UV spectra of Glycyrrhiza glabra and Zingiber officinale are given in Figure 7; Figure 6. Strong absorption peaks are obtained between 203 nm - 232.5 nm, 233 nm - 281nm and 281.5nm - 383nm for Glycyrrhiza glabra . Strong absorption peaks are obtained between 200nm - 257.5nm, 258nm - 290.5nm and 291nm - 366nm for Zingiber officinale.

The strong absorption peaks of Glycyrrhiza glabra and Zingiber officinale UV spectra reveal the presence of some phenolic compounds and flavonoids in the roots of these plants. It has been proved that the maximum UV absorption peak for flavones was lies within 300-380 nm and glycosides, 240-280 nm. A study confirmed the UV absorption of flavanones in the range 270-295 nm (Mabry, 1970).

Glycyrrhiza glabra contains glabridin, the major flavonoid has various physiological activities such as cytotoxic, anti-tumour, antimicrobial, estrogenic and anti-proliferative activity (Khattak & Simpson, 2010). Gingerol is the principle of the pungent nature in Zingiber officinale. Glycrrhiza glabra contains 6-Gingerol as an important gingerol (Zhou, 1998).

The FT-IR spectrum of Glycyrrhiza glabra and Zingiber Officinale are given in Figure 9; Figure 8. The characteristic absorption bands corresponding to the vibration frequencies of 1643.64 cm^-1 and 1647.77 cm^-1 in the IR spectra are due to the carbonyl groups of phenolic compounds. The characteristic absorption bands corresponding to the vibration frequencies of 3284.92 cm^-1 and 3324.99 cm^-1are due to the -OH groups of phenolic compounds and flavonoids present in the Glycyrrhiza glabra and Zingiber officinale roots. The characteristic absorption bands corresponding to the vibration frequencies of 1084.86 cm^-1and 1085.87 cm^-1in the IR spectra are due to the OH bending of the phenolic compounds and flavonoids.

The phyto-chemical groups identified are tabulated in Table 6; Table 5. The vibration frequencies obtained by FT-IR analysis corresponding to –OH group, -OH bending, C=O group, C-H stretch and C-H bends indicate the presence of phenolic compounds, flavanoids and other phytochemicals in the extracts (Kumari & Kumar, 2019).

The root extracts of Glycyrrhiza glabra and Zingiber officinale contain various biologically active functional groups that may belong to diverse compounds which might be responsible for the various biological activities. It has been reported that phenolic components of these medicinal plants such as rutin, glabridin, liquiritin and gingerol have anticancer activities and was able to inhibit cancer cell growth (Elattar & Virji, 2000; Sohi, 2003).

Glycyrrhizin and glycyrrhizic acid, the important phenolic compounds of Glycyrrhiza glabra have been reported for the treatment of HIV-1, hepatitis C. It also functions as an inhibitor of replication in the SARS virus (Cinatl, 2003; Clercq, 2000). Glycyrrihizic acid has also been observed for cytotoxicity against KSHV virus (Curreli, 2005).

Major compounds of Ginger include camphene, b-phellandrene, and 1,8-cineol (Zhou, 1998). Shogaols is found only in semi dried Ginger and found occasionally in fresh Ginger (Bhattarai, 2001; Blaschek, 2013). Other constituents in Zingiber officinale include oleoresins. The presence of these phenolic compounds makes Zingiber officinale a powerful medicinal plant in treating a range of disorders and diseases.

Conclusions

The root components glycyrrhizin and glycyrrhetinic acid are generally regarded as the major biologically active principle of Glycyrrhiza glabra. Gingerol and shogaol, the important phenolic compounds present in the rhizomes of Zingiber officinale are renowned for their contribution to human health and nutrition. The present study was mainly focused on evaluating the activities of flavonoids and phenolic compounds in Glycyrrhiza glabra and Zingiber officinale root extracts. The results obtained have revealed the potential antioxidant and free radical scavenging activities of Glycyrrhiza glabra and zingiber officinale. UV and FT-IR spectral studies pointed out the presence of biologically significant flavonoids and phenolic compounds in the Glycyrrhiza glabra and Zingiber officinale root. Determining the potency of the various chemical components for various biological activities may predict the expected clinical effects of these herbal plants.

Conflict of Interest

The authors declare that they have no conflict of interest for this study.

Funding Support

The authors declare that they have no funding support for this study.